We have the discovered the first small-molecule probes and drug candidates that effectively inhibit the most prevalent S31N drug-resistant mutant of the M2 proton channel of influenza, the target of the marketed anti-flu drugs amantadine and rimantadine. We here propose to exploit our extensive structural biology work in this area to design new, related analogs to increase potency for both the most prevalent mutants and wild-type M2, and to understand and improve drug-like properties to eventually discover new treatments for seasonal influenza infections. Besides the yearly epidemic outbreaks, influenza viruses are even more threatening pathogens due to their potency to cause pandemics, as occurred in 2009 by the emergence and worldwide spread of the H1N1 viruses. Available prophylactic vaccines are not completely effective against emerging flu strains; thus, effective anti-viral therapy is not an adjunct but an essential component of our options in the fight against influenza. Two classes of drugs are currently approved as antiviral agents: the M2 proton channel inhibitors [Symmetrel (amantadine) and Flumadine (rimantadine)] and the neuraminidase inhibitors [Tamiflu (oseltamivir) and Relenza (zanamivir)]. While these drugs are effective in reducing symptomatology from influenza, increasing resistance has severely limited their effectiveness. Resistance to this class of drugs is associated with naturally occurring point mutations in the M2 channel pore, comprised of a single helical strand through the virus outer coat, and four of the M2 proteins taken together form a functional proton channel. The effect of a single mutation is amplified four fold, because it is present in all four of the helices that for the pore. The S31N mutant is the most prevalent and significant amantadine-resistant mutation. It is present in almost all of the currently circulating influenza strains as well as in the avian nd 2009 pandemic H1N1 strains. As a result, there is an urgent need to develop second generation novel M2 inhibitors targeting all clinically relevant mutants of M2, and particularly the most prevalent S31N mutant. Current efforts have already identified several series of novel and potent (in vitro) compounds against S31N as well as other clinically significant M2 variants such as V27A. Our first aim is to optimize the in vitro affinities and drug-like properties of the existng series of M2-S31N inhibitors using iterative medicinal chemistry. We are uniquely situated to do this based upon our understanding as to the 3-D structure of the pore. The second aim is to optimize the in vitro ADME properties of top representative members of different series, for in vivo probe- and drug-like suitability. In Phase II we will advance the most promising lead candidates identified in Phase I through pharmacokinetic profiling, additional ADME and off-target safety studies, and animal efficacy and toxicity tests with the ultimate goal of identifying one or more development candidates. The long term goal of the program is to complete all studies necessary for filing an Investigational New Drug (IND) application.